The present inventions relate to improvements in pressure transducers for use in oil, gas, and geothermal wells, and other subterranean environments. More particularly, the present invention relates to piezoelectric crystal oscillator driven pressure and temperature transducers which are smaller, more accurate during temperature and pressure transient conditions, and respond quicker and with less calibration than those known in the art.
Most physical parameters such as temperature and pressure can be converted into electrical signals by a device known as a transducer. Quartz and some other crystals will oscillate or vibrate at a particular frequency when a driving signal is applied to the crystal. As physical properties of the crystal change as a result of changes in temperature and pressure the vibration frequency changes. In piezoelectric quartz pressure and temperature transducers, the vibration frequency is measured and converted to electrical signals that vary as the pressure and temperature applied to the crystal varies.
It is common practice to use quartz pressure transducers for taking various measurements downhole in various subterranean environments. Quartz pressure transducers or pressure and temperature transducers are typically used in testing wells in order to determine temperature, pressure, and flow rate, from which further information concerning the well can be determined or estimated. Exemplary patents for transducers using temperature, pressure, and reference crystal oscillators are: U.S. Pat. No. 5,471,882 to Wiggins, and U.S. Pat. No. 5,221,873 to Totty, et al., which are incorporated herein for all purposes by this reference.
Conventional measurement systems using quartz oscillator driven transducers in wells are subject to errors caused by static and dynamic pressure and temperature induced errors. For example, physical separation of the quartz sensor and the supporting electronics allows transient temperature errors. No matter how well designed, the output signal or data from a quartz pressure transducer is affected by the temperature of the pressure sensing piezoelectric element, and the data from a temperature sensing quartz element is effected by pressure. It is common to calibrate (correct) pressure data as a function of temperature data collected at or near the pressure-measuring site. Substantial computation is required in order to convert and correct the output into an intelligible form.
Commonly, two crystal sensors are used, both of which are subjected to the temperature of the operating environment, but only one of which is subjected to the pressure parameter to be measured. The output of the temperature sensor is used to calculate the effect of temperature-induced errors on the pressure sensor. Alternatively, a single crystal is used in two different modes of oscillation, i.e., a pressure mode, and a temperature mode. As in the two-sensor method, in this type of arrangement the temperature data is used to adjust the pressure readings to compensate for temperature-induced errors. A reference crystal against which the temperature and pressure signals may be compared is also used in the art. The reference crystal provides a reference signal substantially independent of temperature and pressure that can be used in calibrating signals produced by the temperature and pressure sensors. The piezoelectric pressure sensor is designed to be responsive primarily to changes in pressure. However, piezoelectric pressure sensors in the art are somewhat responsive to changes in temperature. Conversely, the piezoelectric temperature sensor is designed to be responsive primarily to changes in temperature, but piezoelectric temperature sensors in the art are somewhat affected by changes in pressure.
Transducers in the art generally have a metal canister containing sensors, accompanied by electronics external to the transducer body. Alternatively, a larger canister is used, containing both the sensors and electronic components. The size and mass of the canister and separation of the sensor from the circuit result in errors caused by transient conditions.
The present inventions contemplate improved piezoelectric temperature compensated pressure transducers and improved methods for measuring pressure and temperature in a subterranean environment.
The improved apparatus and methods incorporate microelectronic means within the body of a piezoelectric crystal transducer to perform signal processing and/or calibration steps as the physical parameters of pressure and temperature are converted to electrical signals by the transducer sensors. The pressure and temperature data is then stored in or output from the body as a useable pressure or temperature reading.
The present invention provides an improved pressure transducer which outputs more immediate and more accurate pressure and temperature readings than known in the art. The present invention also provides an improved method of minimizing the physical size and mass of the transducer and associated electronics. The reduction of the physical distance between components of the transducer and associated apparatus and the overall reduction in mass, in turn minimize the temperature gradient between pressure sensor element and temperature sensor element. These improvements in signal production and data collection apparatus and methods significantly improve transient response, signal processing and data calibration requirements, and overall accuracy.